There are two ways to look back at the Geneva summit. One is to assume that someone, somewhere, knows what really happened during the two days of meetings between President Reagan and General Secretary Gorbachev and what it all meant. Another is to read the largest of these two volumes and realize that, if history is any guide, there is a good chance that nobody really knows.

That is just one contribution that Raymond L. Garthoff makes, drawing from years of government service, some of it at the eye of the arms control hurricane, years on which he now looks back from his desk at the Brookings Institution in Washington, where he is a senior fellow specializing in Soviet foreign and defense policy.

The smaller of the two volumes is a collection of columns written over a period of three years for Nation magazine by Stephen F. Cohen, a professor of Soviet affairs at Princeton University.

Cohen is another first-rate analyst of the way Americans and Soviets look to one another. His Nation pieces distill views drawn from far more detailed writings of his own and, in fact, one valuable part of the book is a recommended reading list.

Cohen's slim book is like Los Angeles freeway signs that are designed not to show people how to get somewhere but to remind people who already know where they are going that their offramp is approaching. That makes the book no less valuable. For example, he describes Soviet government officials as a collection of conservative elitists, proud and defensive of the Soviet brand of communism, worried that change will make things worse, not better. Most Russians would agree, he writes. That is so profoundly Russian and so contrary to the way the Soviet Union is portrayed most often that this one passage alone is worth not only reading but also committing to memory.

Garthoff's special contribution is his talent for looking at the same event through first American, then Soviet eyes to make it clear how differently they see things. For example, one product of the 1972 Nixon-Brezhnev summit was a document called "Basic Principles of Mutual Relations," in which the two countries agreed, among other things, that there is no alternative to "peaceful coexistence" and that both would do their utmost to "avoid military confrontation." According to Garthoff, the document was drafted by Henry A. Kissinger and his aides in Moscow without consultation with anybody in Washington. President Nixon scarcely mentions it in his reminiscences about the summit and, Garthoff says, may indeed never have read it.

On the other side, the Soviets established an entire new department to implement the agreement and conferred heroes' medals on those who helped write it. For our side, a throwaway; for theirs, something profound and significant.

After the first blush of detente, he writes, Americans worried that getting too cozy with the Soviet Union would be like inviting it to take over the Third World, one country at a time. Some think that is exactly how it has worked out.

And what did the Soviets worry about during those early days of detente? They thought the new relationship would invite an "ideological penetration" of Eastern Europe by the decadent West that would pry Poland and Hungary and the rest loose from socialism.

At one point in fairly recent memory, Washington officials panicked over the inroads of communists in Europe--the Eurocommunists of Italy and other Western nations. If Washington was against Eurocommunism, Moscow must be in favor of it, right? Wrong, says Garthoff. Moscow panicked over the possibility that the Eastern bloc would learn bad habits from Eurocommunists who seemed relatively snug in their bourgeois surroundings. Moscow attacked them as "enemies of Marxism."

And so it goes for 1,147 pages, crammed with footnotes as addictive as peanuts, while Garthoff peers like a referee along the line of scrimmage between East and West, over a period stretching from Richard Nixon to Ronald Reagan. He roots for the home team, but he sees the offsides and fumbles on both sides.

One of Garthoff's important themes is that arms control has not failed political leaders in this country, political leaders have failed arms control. In 1972, he writes, Nixon and Brezhnev agreed in private at the summit that led to the arms control agreement known as SALT I that both sides would be free to push ahead with military preparations, including nuclear weapons, that were not explicitly covered by the agreement. But because Nixon did not say much if anything about that agreement in the United States, opponents of arms control could use every new piece of Soviet military hardware as evidence that Moscow was reneging on arms control.

In negotiations leading up to the next arms control agreement, SALT II, U.S. negotiators were less than candid with the American public about a Soviet bomber known in this country as the Backfire. The negotiators agreed with the Soviets that it did not have the range to reach U.S. targets and therefore would not be counted in the ceilings on strategic weapons. But they did not stand up for that position publicly against opponents who just kept saying again and again that Backfire was an intercontinental bomber. It was one of the arguments that made it impossible for the Senate to ratify SALT II.

It probably is impossible to write a single book containing everything worth knowing about arms control and what it all means for the future. But Garthoff has made a heroic effort.